1. Field of the Invention
This invention relates to a capacitance type displacement measuring probe for measuring the vibrations of a dynamoelectric machine.
2. Description of the Prior Art
It is necessary at the time a large dynamoelectric machine is manufactured and from time to time thereafter to check the machine and more particularly the rotor thereof for vibration. Since a dynamoelectric machine is susceptible to vibration, if excessive vibration occurs and is permitted to continue, the dynamoelectric machine may be damaged. Existing devices employed to measure the vibrations of a dynamoelectric machine are of several types. Devices of one type measure the vibration of the dynamoelectric machine by contacting a rotating member, such as the rotor, of the dynamoelectric machine and producing a signal proportional to the velocity of the rotating member. A disadvantage of the devices of this type is that chatter occurs as a result of the contact between the device and the rotating member.
Devices of a second type measure the vibration of a dynamoelectric machine by measuring the velocity of the rotor or rotating member of the dynamoelectric machine and producing a signal proportional to the vibration of the rotor of the machine. A disadvantage of measuring vibration in this manner is that devices of this type detect a change in vibration only if there is a change in the velocity of the rotating member. If velocity of the rotating member remains constant, the device will not detect a change in the vibration of the rotating member and thus the dynamoelectric machine may be damaged.
Another type of device measures the vibration of a dynamoelectric machine by measuring the change in capacitance of a capacitor formed by the device and a rotating collector ring of the dynamoelectric machine. A change in distance between the collector ring and the device caused by a change in vibration of the dynamoelectric machine is reflected as a change in capacitance. However, devices of this type only scan a locus of points around the collector ring and thus can accurately measure vibration only if the collector ring has a smooth surface. If a helical groove is placed in the surface of the collector ring, as is now common practice, for the purpose of avoiding uneven electrical brush wear, then this latter type device is unusable. Further, the accuracy of devices of this type is adversely affected by stray capacitance between the probe and other elements of the dynamoelectric machine.
By utilizing the capacitance displacement probe of the present invention, in a manner hereinafter more fully described, vibration of the rotor of a dynamoelectric machine can be measured without contacting the rotor, thereby avoiding the chatter that occurs as a result of direct contact between the probe and the rotor. Further, by utilizing the capacitance displacement probe of the present invention, the vibration of the rotor of a dynamoelectric machine can be accurately measured irrespectively of the velocity or change of velocity of the rotor. Further, by utilizing the probe of the present invention, vibration of the rotor of a dynamoelectric machine can be measured when a helical groove is utilized on the surface of a collector ring associated with the rotor. In addition, by utilizing the probe of the present invention, the vibration of the rotor of a dynamoelectric machine can be measured without the measurement being adversely affected by stray capacitance.
Accordingly, it is an object of this invention to provide a new and improved capacitance displacement measuring probe that measures the vibration of a dynamoelectric machine without contacting any rotating members of the dynamoelectric machine.
Another object of this invention is to provide a capacitance displacement measuring probe that accurately measures the vibrations of the rotor of a dynamoelectric machine irrespective of the velocity or change of velocity of the rotor of the dynamoelectric machine.
A further object of this invention is to provide a capacitance displacement measuring probe that measures the vibration of a rotor of a dynamoelectric machine wherein a collector ring associated with said rotor has a helical groove therein.
Another object of this invention is to provide a capacitance displacement measuring probe that measures the vibration of the rotor of a dynamoelectric machine without being adversely affected by stray capacitance.